Antimicrobial activity of Mexican oregano (Lippia berlandieri), thyme (Thymus vulgaris), and mustard (Brassica nigra) essential oils in gaseous phase

Abstract

The antimicrobial efficacy of essential oils (EOs) when applied in gaseous phase depends on the volatility of their compounds and their corresponding antimicrobial activities. The antimicrobial activity of EOs from Mexican oregano (Lippia berlandieri), thyme (Thymus vulgaris), or mustard (Brassica nigra) against a panel of bacterial and fungal species was studied by gaseous contact. Chemical composition of EOs was analyzed by gas chromatography coupled to mass spectrometry. The minimum inhibitory concentration (MIC) for each EO was determined by the inverted-dish technique. Results showed that the tested EOs displayed significant (p < 0.05) antimicrobial effects with MICs in the range of 0.012–1.0 μg/mL of air. Identified compounds in the oils suggest that allyl isothiocyanate (in mustard EO); p-cymene, linalool, and thymol (in thyme EO); and p-cymene and carvacrol (in oregano EO) were the active compounds with antimicrobial activities. Evaluated microorganisms exhibited different sensitivity to tested EOs in gaseous phase, but bacterial strains are the most resistant to thyme and oregano EOs. The cytotoxicity and the immune response of the EOs were also evaluated using a human model of macrophages. Results of this study suggest that these EOs can be used as an alternative to antimicrobial agents in processed or packaged food because of the high volatility of their compounds with strong inhibitory effects.